diff --git a/docmd/theory/kmers.md b/docmd/kmers.md
similarity index 100%
rename from docmd/theory/kmers.md
rename to docmd/kmers.md
diff --git a/src/.~lock.Synthese.docx# b/src/.~lock.Synthese.docx#
new file mode 100644
index 0000000..6631e2a
--- /dev/null
+++ b/src/.~lock.Synthese.docx#
@@ -0,0 +1 @@
+Eric Coissac,coissac,mac.lan,20.04.2026 19:13,file:///Users/coissac/Library/Application%20Support/LibreOffice/4;
\ No newline at end of file
diff --git a/src/Cargo.lock b/src/Cargo.lock
index ce0c031..78bb33b 100644
--- a/src/Cargo.lock
+++ b/src/Cargo.lock
@@ -8,6 +8,15 @@ version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "320119579fcad9c21884f5c4861d16174d0e06250625266f50fe6898340abefa"
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ddd31a130427c27518df266943a5308ed92d4b226cc639f5a8f1002816174301"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "anes"
 version = "0.2.1"
@@ -541,6 +550,15 @@ version = "0.4.29"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5e5032e24019045c762d3c0f28f5b6b8bbf38563a65908389bf7978758920897"
 
+[[package]]
+name = "matchers"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d1525a2a28c7f4fa0fc98bb91ae755d1e2d1505079e05539e35bc876b5d65ae9"
+dependencies = [
+ "regex-automata",
+]
+
 [[package]]
 name = "memchr"
 version = "2.8.0"
@@ -571,6 +589,15 @@ dependencies = [
  "zstd",
 ]
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "num-traits"
 version = "0.2.19"
@@ -623,6 +650,8 @@ version = "0.1.0"
 dependencies = [
  "niffler",
  "obikrope",
+ "tracing",
+ "tracing-subscriber",
  "ureq",
 ]
 
@@ -659,6 +688,12 @@ version = "2.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "9b4f627cb1b25917193a259e49bdad08f671f8d9708acfd5fe0a8c1455d87220"
 
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
 [[package]]
 name = "pkg-config"
 version = "0.3.33"
@@ -724,6 +759,23 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "regex-automata"
+version = "0.4.14"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e1dd4122fc1595e8162618945476892eefca7b88c52820e74af6262213cae8f"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc897dd8d9e8bd1ed8cdad82b5966c3e0ecae09fb1907d58efaa013543185d0a"
+
 [[package]]
 name = "ring"
 version = "0.17.14"
@@ -825,6 +877,15 @@ dependencies = [
  "zmij",
 ]
 
+[[package]]
+name = "sharded-slab"
+version = "0.1.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f40ca3c46823713e0d4209592e8d6e826aa57e928f09752619fc696c499637f6"
+dependencies = [
+ "lazy_static",
+]
+
 [[package]]
 name = "shlex"
 version = "1.3.0"
@@ -909,6 +970,15 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "thread_local"
+version = "1.1.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f60246a4944f24f6e018aa17cdeffb7818b76356965d03b07d6a9886e8962185"
+dependencies = [
+ "cfg-if",
+]
+
 [[package]]
 name = "tinystr"
 version = "0.8.3"
@@ -919,6 +989,67 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "tracing"
+version = "0.1.44"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "63e71662fa4b2a2c3a26f570f037eb95bb1f85397f3cd8076caed2f026a6d100"
+dependencies = [
+ "pin-project-lite",
+ "tracing-attributes",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-attributes"
+version = "0.1.31"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7490cfa5ec963746568740651ac6781f701c9c5ea257c58e057f3ba8cf69e8da"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "tracing-core"
+version = "0.1.36"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
+dependencies = [
+ "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
+]
+
+[[package]]
+name = "tracing-subscriber"
+version = "0.3.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb7f578e5945fb242538965c2d0b04418d38ec25c79d160cd279bf0731c8d319"
+dependencies = [
+ "matchers",
+ "nu-ansi-term",
+ "once_cell",
+ "regex-automata",
+ "sharded-slab",
+ "smallvec",
+ "thread_local",
+ "tracing",
+ "tracing-core",
+ "tracing-log",
+]
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.24"
@@ -971,6 +1102,12 @@ version = "0.2.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "06abde3611657adf66d383f00b093d7faecc7fa57071cce2578660c9f1010821"
 
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
 [[package]]
 name = "walkdir"
 version = "2.5.0"
diff --git a/src/Synthese.docx b/src/Synthese.docx
new file mode 100644
index 0000000..79b1209
Binary files /dev/null and b/src/Synthese.docx differ
diff --git a/src/obiread/Cargo.toml b/src/obiread/Cargo.toml
index d182b93..8310c68 100644
--- a/src/obiread/Cargo.toml
+++ b/src/obiread/Cargo.toml
@@ -7,3 +7,5 @@ edition = "2024"
 obikrope = { path = "../obikrope" }
 niffler = { version = "2", default-features = false, features = ["gz", "bz2", "lzma", "zstd"] }
 ureq   = "2"
+tracing = "0.1.44"
+tracing-subscriber = { version = "0.3.23", features = ["fmt", "env-filter"] }
diff --git a/src/obiread/examples/expand_path.rs b/src/obiread/examples/expand_path.rs
new file mode 100644
index 0000000..e47d89d
--- /dev/null
+++ b/src/obiread/examples/expand_path.rs
@@ -0,0 +1,20 @@
+use obiread::expand_paths;
+use tracing::{info, subscriber};
+use tracing_subscriber::{EnvFilter, fmt};
+
+fn main() {
+    // Build a subscriber with environment-based filtering
+    tracing_subscriber::fmt()
+        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
+        .init();
+
+    info!("Expanding paths...");
+    let paths = vec![
+        "/home/user/data".to_string(),
+        "/home/user/sample.fastq.gz".to_string(),
+    ];
+    let files = expand_paths(&paths);
+    for f in files {
+        println!("{}", f.display());
+    }
+}
diff --git a/src/obiread/src/lib.rs b/src/obiread/src/lib.rs
index 47f438a..5476b99 100644
--- a/src/obiread/src/lib.rs
+++ b/src/obiread/src/lib.rs
@@ -5,12 +5,15 @@
 
 #![deny(missing_docs)]
 
+pub mod chunk;
 mod fasta;
 mod fastq;
-pub mod chunk;
+mod list_of_files;
 pub mod normalize;
 pub mod xopen;
 
+pub use list_of_files::expand_paths;
+
 use std::io::Read;
 
 use chunk::SeqChunkIter;
diff --git a/src/obiread/src/list_of_files.rs b/src/obiread/src/list_of_files.rs
new file mode 100644
index 0000000..f87ef81
--- /dev/null
+++ b/src/obiread/src/list_of_files.rs
@@ -0,0 +1,47 @@
+use std::fs;
+use std::path::Path;
+use std::path::PathBuf;
+use tracing::info;
+
+/// Returns true if the path ends with a fasta or fastq file extension.
+fn is_fasta_or_fastq(path: &Path) -> bool {
+    let name = path.file_name().and_then(|n| n.to_str()).unwrap_or("");
+    name.ends_with(".fasta")
+        || name.ends_with(".fa")
+        || name.ends_with(".fastq")
+        || name.ends_with(".fq")
+        || name.ends_with(".fasta.gz")
+        || name.ends_with(".fa.gz")
+        || name.ends_with(".fastq.gz")
+        || name.ends_with(".fq.gz")
+}
+
+/// Walks a directory, collecting fasta or fastq files into the output vector.
+fn walk_dir(dir: &Path, out: &mut Vec<PathBuf>) {
+    if let Ok(entries) = fs::read_dir(dir) {
+        for entry in entries.flatten() {
+            let path = entry.path();
+            if path.is_dir() {
+                walk_dir(&path, out);
+            } else if path.is_file() && is_fasta_or_fastq(&path) {
+                out.push(path);
+            }
+        }
+    }
+}
+
+/// Expands a list of paths, returning a vector of `PathBuf` for fasta or fastq files.
+pub fn expand_paths(paths: &[String]) -> Vec<PathBuf> {
+    let mut result = Vec::new();
+    for path_str in paths {
+        info!("Current step: {}", path_str);
+        let path = Path::new(path_str);
+        if path.is_dir() {
+            walk_dir(path, &mut result);
+        } else if path.is_file() && is_fasta_or_fastq(path) {
+            info!("Found fasta or fastq file: {}", path_str);
+            result.push(path.to_path_buf());
+        }
+    }
+    result
+}